The present invention pertains to composite wires reinforced with substantially continuous fibers within a metal matrix and cables incorporating such wires.
Metal matrix composite""s (MMC""s) have long been recognized as promising materials due to their combination of high strength and stiffness combined with low weight. MMC""s typically include a metal matrix reinforced with fibers. Examples of metal matrix composites include aluminum matrix composite wires (e.g., silicon carbide, carbon, boron, or polycrystalline alpha alumina fibers in an aluminum matrix), titanium matrix composite tapes (e.g., silicon carbide fibers in a titanium matrix), and copper matrix composite tapes (e.g., silicon carbide fibers in a copper matrix).
The use of some metal matrix composite wires as a reinforcing member in bare overhead electrical power transmission cables is of particular interest. The need for new materials in such cables is driven by the need to increase the power transfer capacity of existing transmission infrastructure due to load growth and changes in power flow due to deregulation.
The availability of wires having a round cross-section is desirable in providing cable constructions that are more uniformly packed. The availability of round wires having a more uniform diameter along their length is desirable in providing cable constructions having a more uniform diameter. Thus, there is a need for a substantially continuous metal matrix composite wire having a round cross-section and uniform diameter.
The present invention relates to substantially continuous fiber metal matrix composites. Embodiments of the present invention pertain to metal matrix composites (e.g., composite wires) having a plurality of substantially continuous, longitudinally positioned fibers contained within a metal matrix. Metal matrix composites according to the present invention are formed into wires exhibiting desirable properties with respect to elastic modulus, density, coefficient of thermal expansion, electrical conductivity, and strength.
The present invention provides a metal matrix composite wire that includes at least one tow (typically a plurality of tows) comprising a plurality of substantially continuous, longitudinally positioned fibers in a metal matrix. The fibers are selected from the group of ceramic fibers, carbon fibers, and mixtures thereof. Significantly, the wire has certain roundness, roundness uniformity, and/or diameter uniformity characteristics over specified lengths.
One preferred embodiment of the present invention is a metal matrix composite wire comprising at least one tow (typically a plurality of tows) comprising a plurality of at least one of substantially continuous, longitudinally positioned ceramic or carbon fibers in a metal matrix, wherein the wire has a roundness value of at least 0.9, a roundness uniformity value of not greater than 2%, and a diameter uniformity value of not greater than 1% over a length of at least 100 meters (preferably, at least 200 meters, more preferably, at least 300 meters). Preferably, in increasing order of preference, the roundness value is at least 0.91, 0.92, 0.93, 0.94, or 0.95; the roundness uniformity value is not greater than 1.9%, 1.8%, 1.7%, 1.6%, or 1.5%, and the diameter uniformity value is not greater than 0.95%, 0.9%, 0.85%, 0.8%, 0.75%, 0.7%, 0.65%, 0.6%, 0.55%, or 0.5. Typically, the roundness value is preferably in the range from about 0.92 to about 0.95.
Another preferred embodiment of the present invention is a metal matrix composite wire comprising at least one tow (typically a plurality of tows) comprising a plurality of at least one of substantially continuous, longitudinally positioned ceramic or carbon fibers in a metal matrix, wherein the wire has a roundness value of at least 0.85, a roundness uniformity value of not greater than 1.5%, and a diameter uniformity value of not greater than 0.5% over a length of at least 100 meters (preferably, at least 200 meters, more preferably, at least 300 meters). Preferably, in increasing order of preference, the roundness value is at least 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, or 0.95; the roundness uniformity value is not greater than 1.4%, 1.3%, 1.2%, 1.1%, or 1%; and the diameter uniformity value is not greater than 0.85%, 0.8%, 0.75%, 0.7%, 0.65%, 0.6%, 0.55%, or 0.5%. Typically, the roundness value is preferably in the range from about 0.92 to about 0.95.
In another embodiment, there is provided a method of making the composite wires according to the present invention. This method includes providing a contained volume of molten metal matrix material; immersing at least one tow (typically a plurality of tows) comprising a plurality of substantially continuous fibers into the contained volume of melted matrix material, wherein the fibers are selected from the group of ceramic fibers, carbon fibers, and mixtures thereof; imparting ultrasonic energy to cause vibration of at least a portion of the contained volume of molten metal matrix material to permit at least a portion of the molten metal matrix material to infiltrate into the plurality of fibers such that an infiltrated plurality of fibers is provided; and withdrawing the infiltrated plurality of fibers from the contained volume of molten metal matrix material under conditions which permit the molten metal matrix material to solidify to provide metal matrix composite wire according to the present invention.
In yet another embodiment, there is provided a cable that includes at least one metal matrix composite wire according to the present invention. Advantages of embodiments of wires according to the present invention in cable constructions allow, for example, more uniform packing of wires in the inner layers of the cable, due to the shape and diameter uniformity of the wire. Such shape and diameter uniformity also tend to reduce cable defects such as gaps between wires, or pinched wires, for example in the outer wire layers.
As used herein, the following terms are defined as:
xe2x80x9cSubstantially continuous fiberxe2x80x9d means a fiber having a length that is relatively infinite when compared to the average fiber diameter. Typically, this means that the fiber has an aspect ratio (i.e., ratio of the length of the fiber to the average diameter of the fiber) of at least about 1xc3x97105, preferably, at least about 1xc3x97106, and more preferably, at least about 1xc3x97107. Typically, such fibers have a length on the order of at least about 50 meters, and may even have lengths on the order of kilometers or more.
xe2x80x9cLongitudinally positionedxe2x80x9d means that the fibers are oriented in the same direction as the length of the wire.
xe2x80x9cRoundness value,xe2x80x9d which is a measure of how closely the wire cross-sectional shape approximates a circle, is defined by the mean of the measured single roundness values over a specified length, as described in the Examples, below.
xe2x80x9cRoundness uniformity value,xe2x80x9d which is the coefficient of variation in the measured single roundness values over a specified length, is the ratio of the standard deviation of the measured single roundness values divided by the mean of the measured single roundness values, as described in the Examples, below.
xe2x80x9cDiameter uniformity value,xe2x80x9d which is the coefficient of variation in the measured average diameters over a specified length, is defined by the ratio of the standard deviation of the measured average diameters divided by the mean of the measured average diameters, as described in the Examples, below.